Ex Parte Quirin
In Ex Parte Quirin 317 U.S. 1 (1942), the United States Supreme Court ruled that in times of war, enemy combatants can be tried in military courts.
In 1942, eight agents of Germany infiltrated the United States with explosives intent on destroying war factories. One contingent of these agents was sighted in New York by a member of the Coast Guard, but the contingent escaped when the Coast Guard member went to get reinforcements. One of the Germans, George Dasch, apparently realized that the mission was in jeopardy and went to Washington to turn himself and his comrades in to the FBI. The military quickly initiated a trial of the men, but one member of the defense, Kenneth Royall, disputed the constitutionality of the process. Hence the matter was brought to the Supreme Court. As a result of the ruling, the men were tried and found guilty in military court. Six were executed and two were sentenced to long prison terms.